The cluster of a background is specified among a plurality of clusters classified by clustering processing, and a label area whose size is less than a first threshold value is combined with adjoining another label area which is not the cluster of the background among label areas to which the same label number is given by labeling processing. Then, whether the label area is combined with the adjoining another label area based on characteristic quantity obtained from the label area is determined, and combining, vector data is generated based on the label area after combining the label area when determined as the label area being combined.